This invention generally relates to a detection system using fiber optics. More particularly, this invention relates to a detection system using a plurality of fiber optic elements wherein each fiber optic element has a light input thereto having a unique frequency or digital code. When a break occurs in one or more fiber optic elements, the missing light frequencies or digital codes are sensed, thereby indicating the break. This invention is particularly well suited for use in grid configurations wherein precise location of the breaks can be made.
There is a great need for detections systems which detect certain events in remote or inaccessible environments. These environments may be remote because they pose a health hazard or because they are inaccessible so that direct assessment of the event is impossible. For example, there is a need to monitor and detect events such as leakage or breakage in hazardous waste containment and disposal systems; as well as nuclear (e.g. radioactive) environments. Similarly, in many remote impact experiments and tests, a direct assessment of the damage test results is impossible. Thus, a system is needed to provide real-time impact information. An illustrative example of such a test would be an intercept test involving a rocket launched warhead intercepting a reentry vehicle at high altitude. It will be appreciated that under experimental conditions there is a need to place a hit-indicator system on board the reentry vehicle to monitor the effectiveness of the interceptor.
Still another example of important applications for remote detection systems is in security systems. Security systems often include a security fence or the like installed along a perimeter or a boundary. In the event of a breach of the security system, the fact of the breach is signaled by an alarm. With the present invention, the location of the breach may also be immediately known.
There are known systems for detecting certain events in remote environments which utilize a plurality of fiber optic elements as an integral component thereof. Such known systems are disclosed in U.S. Pat. Nos. 4,399,430; 4,450,434; and 4,581,527.
U.S. Pat. No. 4,581,527 discloses a grid or array of optical fibers in a series of layers for locating and assessing damage in a structure (e.g. plastic composite structure). Light from a single light source is inputted through the fibers in a planar array, and an optoelectronic viewing device analyzes the fiber output from that planar array. In the event of damage to the structure, broken fibers will not carry light. The location of the damaged area (e.g. broken fibers) in two dimensions in any given plane is determined from those fibers having dark outputs. An LED may be used as the light source. The damage in three dimensions may be determined by performing the two dimensional analysis in the several layers.
U.S. Pat. No. 4,399,430 describes a security system incorporating a mesh-like array of fiber optic elements. When an element is broken, light will cease passing therethrough which will trigger an alarm. However, there is no disclosure of means for determining the location of the broken element(s). U.S. Pat. No. 4,450,434 describes a security device which is similar to the device of U.S. Pat. No. 4,399,430, however it does provide means for determining the location of the break. This is accomplished by using time domain reflectometry (TDR) techniques which measures the time it takes for a train of pulses to travel to the break in the fiber optic element and then be reflected back.
Notwithstanding the above-described prior fiber optic detection systems, there is a continuing need for improved fiber optic detection systems which will provide accurate information about the location and time of a break, and which are more reliable, simpler in design and more cost effective to manufacture and operate than the prior art.